This invention relates generally to steam pressure cookers or the like particularly to an improved drain and venting system therefor.
Steam or pressure-type cookers have been successfully employed by restaurants, hospitals and other food service operations to prepare quickly and conveniently large quantities of food. They are especially convenient for the preparation of frozen foods, and in such use incorporate a defrosting step as an initial part of the cooking process. Typical such steam cookers are illustrated by Churley U.S. Pats. No. 3,071,063 and No. 3,071,473. Such cookers subject the food placed in trays in the cooker vessel to jets of steam which may impinge directly upon the food in an atmosphere above atmospheric pressure, thus thawing and cooking the food rapidly.
Typically, the drain system for prior art steam cookers has consisted of a drain pipe located in the bottom of the pressure treatment vessel and fitted with a solenoid operated drain valve. The pipe can empty into an open bell fitting which is connected with the building waste system. The drain pipe, or the drain valve, has a predetermined relatively small flow capacity, correlated to the flow capacity of the steam inlet to the vessel. Once food in the cooker is thawed (defrosted), the rate of steam condensation in the vessel slows noticeably and, as a result of the limited drain capacity, pressure (and temperature) in the cooker begins to rise. The rise in pressure or temperature is sensed by an appropriate sensor device, and the drain valve is closed in response thereto. Thus, since termination of the defrosting cycle and commencement of the cooking cycle depends upon pressure buildup (or temperature rise) the drain pipe and drain valve are necessarily of a size small enough to restrict steam outflow and allow the pressure to build in the vessel at the end of the defrost cycle.
In using a cooker of this type it is found that food particles may fall from a cooking pan in the cooker and be carried into the drain with exhausting steam, particularly at the end of a cooking cycle, and these particles can clog the relatively small drain pipe and valve. As a result, a clogged drain may render the cooker inoperative, since the defrost cycle is prevented from operating properly. Therefore, prior art drain systems must be periodically disassembled, checked and cleaned of food particles that could plug the drain system, particularly the drain valve.
Inclusion of an additional drain valve, e.g., as shown in U.S. Pat. No. 3,804,591 to Bezrodny et al, will not provide a solution for this possibility. The autoclave shown in the Bezrodny patent has a single regulated exhaust with two control valves in series in the exhaust to control pressure in the autoclave, and a water drain valve in the bottom of the autoclave. Although the size and use of the water drain valve are not specified in the Bezrodny patent, it is apparent that these elements are used only after the autoclave has cooled and depressurized. In a food service operation such a long period for depressurization and cool down would be a disadvantage since quick and convenient operation is desired.
The use of multiple pressure vessel outlet lines, such as a defrost line and a drain line, along with appropriate solenoid operated valves and control circuitry, is disclosed in the aforementioned related application, and provides a generally satisfactory solution to the problem of removal of food particles from the cooker without interfering with or preventing the operation of a restricted flow means which allows the cooker to operate with a defrost cycle. However, such an arrangement does not provide for interruption once the cycle has begun. If, for some unknown reason, the bottom drain becomes blocked, or the valve malfunctions, there will be no effective draining from the cooker, and it generally cannot be opened immediately.
A cooker with a blocked drain is inconvenient, but is not necessarily unsafe since it will in a reasonable time cool and depressurize as steam in the cooker condenses. The cooker however, will upon cool down remain under slowly decreasing out pressure so that the door will be openable only by prying an edge from its seal to release pressure. As can be appreciated, such a situation is inconvenient and the cooker, especially the door or its seal, can be damaged by the use of a prying instrument.
In some cooker use situations it is desirable to interrupt the cooking cycle temporarily in order to, for example, add or remove food having different cooking time. Although depressurization and door opening in this instance could be accomplished by cancelling the time remaining on the timer followed by resetting the timer after the cooker has been reclosed, it is desirable that some means independent of the timer be provided for such occasions.